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Messages - garyhlucas

541
Tangent Corner / Re: Thread Milling cutters
« on: January 16, 2014, 06:24:39 PM »
Yep,
You can make any pitch, inside or outside in nearly any diameter with just one tool, like a lathe. It is slower than tapping in the small sizes most of the time, but comes into it's own on parts like what you are making where even if you could afford the tap you'd probably have no way to turn it!

542
Tangent Corner / Re: Thread Milling cutters
« on: January 16, 2014, 09:32:18 AM »
Yes you can do internal and external threads with the same tool, but it has to fit into the hole for internal threads.  Thread milling is great for tapered pipe threads because the diameters are large relative to the thread length and it takes huge torque to use a tap and die on a pipe thread.

543
Tangent Corner / Re: Thread Milling cutters
« on: January 16, 2014, 09:29:36 AM »
Yes regular taps need the Z axis synchronized with the spindle. Thread milling is just a spiral milling operation, X, Y and Z are synchronized already.

544
Tangent Corner / Re: Thread Milling cutters
« on: January 15, 2014, 10:13:59 PM »
You don't need a VFD or spindle encoder to do thread milling with a single point tool. On a lathe you need an encoder. Thread milling is done with a spiral tool path. Typically you want to spiral upwards from the bottom of the hole, because you are climbing out of the chips instead diving into them.

545
General Mach Discussion / Re: How fast?
« on: January 12, 2014, 01:52:28 PM »
The only reason I might have for moving fast is that I am mounting an extruder head on the machine for 3D printing. From what I a have seen on the 3D printer forums they are mostly low mass moving fast.  So I will probably have what is a relatively slow but very accurate 3D printer.  We will know soon as I plan on installing the extruder shortly.

546
General Mach Discussion / How fast?
« on: January 11, 2014, 11:31:06 PM »
I've had my CNC mill running for about 6 months and tuned the motors for 100 ipm rapids.  It has 18 inches of travel on all three axis. However I got wondering about how quick it might actually be able to run.  So today I played a little with motor tuning.  My axis are all driven by 20 mm x 5 mm pitch ball screws and the ways are THK recirculating ball type.  I have a Xilufeng USB breakout board driving Leadshine 80 volt steppers with a 68vdc power supply.  The motors are Nema 34 860in/oz holding torque.  Z axis mass is about 50 lbs, Y axis is 40 lbs and X axis is 85 lbs with a stationary 205 lb table.

I was able to tune it to work well with all axis running at 320 steps/mm, 8700mm/min and acceleration set at 2200.  That's a stepper motor speed of 1740 rpm, and 342 in/min rapids.  Its a little scary watching it move at those speeds!  Is this a good rate or are some you running much faster?  I tuned it back down because I have my grandson working with me and I don't see actually cutting at those speeds.

547
My machine has very long cables due to the physical design. I spent a fortune on shielded cables (Igus), one ground point, high voltage and low voltage in separate metal enclosures, wires crossing at right angles etc.  Not a glitch anywhere, ever, until I added two little solenoid valves last week for air and coolant, with shielded cables and isolation relays too.  When either valve turned off all the axis would jump like a full step!  A flyback diode across the solenoid coils took care of it though. Surprised the heck out of me though.

548
General Mach Discussion / Re: Cannot get to 200 IPM
« on: January 06, 2014, 06:29:36 PM »
I'd look at the voltage when the X axis is moving. I see that the power supply is a switcher and it may simply reduce the output voltage if it asked to supply more than rated current.  I suspect this because you seem to only have the problem with two motors running at the same time. Also has someone else said the motors you have are high inductance so the back emf rises quickly and the torque falls way off as a result.  Lower inductance motors can run faster at the same voltage.

549
Show"N"Tell ( Your Machines) / Re: mach3 3D printer
« on: January 05, 2014, 09:58:57 PM »
Looks good,

I'm working on doing the same thing.  My machine is a little bigger 18" x 18" x 18" travels and Nema 34 steppers running on 68vdc. I have a 12" square heated bed but the extruder isn't mounted yet as I am making new parts for it.  It was a really poor design as recieved.  All the wiring is already installed, I just need to make a few connections and update the PLC code to work the extruder and heated bed.

http://s811.photobucket.com/user/garyhlucas/library/?sort=2&page=1

In the pictures you can see a lathe tool post behind the spindle.  The extruder mounts just behind that.  So with no tool in the spindle or tool mounted for the lathe the extruder is the lowest point.  Installing a mill tool or a lathe tool makes that the lowest point.  So in theory I can clean up a printed gear with the mill and use a shaping tool on the lathe tool post to cut a key in it, without moving the part.

550
General Mach Discussion / Re: Rigid Tapping
« on: January 05, 2014, 09:30:55 AM »
While I would agree that an inexpensive VFD and encoder might be set up such that the Z follows it to a random stop position, that is simply not true of many VFD drives out there. A good VFD can produce 100% of rated torque in braking and stop exactly where you want it to.  Lots of them are used in positioning applications.